BACKGROUND OF THE INVENTION
1. Field of the Invention
[0001] This specification relates to a motor drive system that drives a motor as one of
power sources of a vehicle, and a method of controlling the motor drive system.
2. Description of Related Art
[0002] In an electrically powered vehicle, such as an electric vehicle or a hybrid vehicle,
a motor is installed as one of its power sources. The motor is driven by a motor drive
system including an inverter and a control unit. The inverter switches a plurality
of switching devices between ON and OFF, so as to convert direct-current (DC) power
into alternating-current (AC) power, and deliver the AC power to the motor. The control
unit produces a switching signal of the inverter, by comparing a modulating wave indicating
a command value for the motor, with a carrier wave.
[0003] When rotation of the motor is disturbed or hampered by external force, and the motor
is brought into a locked state, electric current concentrates in a winding of only
one phase, among windings provided in the motor. In this case, switching devices corresponding
to this phase, among the switching devices provided in the inverter, rapidly generate
heat. Thus, it has been proposed to determine that the motor is in the locked state
when its rotational speed becomes equal to or lower than a predetermined speed, and
change the frequency of the carrier wave (which will be called "carrier frequency")
to a particularly low protection frequency.
[0004] However, the rotational speed of the motor is reduced not only in the case where
the motor is locked, but becomes temporarily equal to or lower than the predetermined
speed in the course of acceleration or deceleration. If the carrier frequency is changed
to the protection frequency when the motor speed temporarily passes a low-speed region
as in this case, a noise problem may be created.
[0005] Thus, a technology for protecting switching devices while preventing the noise is
described in Japanese Unexamined Patent Application Publication No.
2000-134990 (
JP 2000-134990 A). More specifically, in a control system of
JP 2000-134990 A, a temperature sensor is provided for detecting the temperature (device temperature)
of the switching devices, and a determination line that indicates criteria for determination
as to which combination of the device temperature and a torque command value requires
the carrier frequency to be changed to the protection frequency is obtained in advance.
Then, when the motor speed becomes equal to or lower than a predetermined threshold
value, the device temperature and torque command value at this point in time are compared
with the determination line, and the carrier frequency is changed to the protection
frequency if the device temperature and the torque command value become greater than
the determination line.
[0006] With the control system of
JP 2000-134990 A, even when the rotational speed of the motor becomes equal to or lower than the predetermined
threshold value, the carrier frequency is not changed to the protection frequency
unless the device temperature and the torque command value become greater than the
determine line. As a result, the carrier frequency is not changed to the protection
frequency when the motor passes a low-speed region only temporarily; therefore, unnecessary
noise can be effectively prevented from being generated. United States Patent Application
Publication N°
2007/114965 A1 relates to an electrically powered vehicle mounting electric motor and control method
therefor comprising the features of the preambles of the independent claims.
SUMMARY OF THE INVENTION
[0007] However, when the system is configured to change the carrier frequency in view of
the device temperature, as in
JP 2000-134990, it is naturally necessary to provide a temperature sensor separately. The addition
of the temperature sensor results in increase of the cost, and increase of the number
of steps for maintenance of components.
[0008] Thus, the present invention provides a motor drive system that achieves both prevention
of overheating of switching devices, and prevention of unnecessary noise, without
requiring a temperature sensor to be added, and a method of controlling the motor
drive system.
[0009] A first aspect of the invention is concerned with a motor drive system. The motor
drive system includes a motor for driving a vehicle, an inverter, and an electronic
control unit. The inverter includes a plurality of switching devices, and is configured
to convert direct-current power into alternating-current power. The electronic control
unit is configured to generate a switching signal of each of the switching devices,
by performing, based on a carrier wave, pulse-width modulation of a modulating wave
indicating a command value for the motor. The electronic control unit is configured
to change a carrier frequency as a frequency of the carrier wave, according to operating
conditions of the motor. The electronic control unit is configured to set the carrier
frequency to a protection frequency for protecting the switching devices, when the
motor is in a first state in which an operating point determined by a rotational speed
of the motor and torque of the motor lies in a lock region that is defined in advance,
and the motor is not in an accelerating or decelerating state The electronic control
unit is configured to set the carrier frequency to a non-protection frequency that
is higher than the protection frequency, when the motor is in a second state in which
the operating point lies in the lock region, and the motor is in the accelerating
or decelerating state.
[0010] With the above configuration, when the motor is in an accelerating or decelerating
state, the carrier frequency is set to the non-protection frequency even when the
motor operating point lies in the lock region. It is thus possible to prevent a noise
problem that would arise when the motor operating point temporarily enters the lock
region in the course of acceleration or deceleration, and the carrier frequency is
changed to the protection frequency. Also, with the above configuration, no temperature
sensor is needed, and the number of components can be prevented from being increased.
[0011] In the motor drive system, the electronic control unit may be configured to store
a map for locked state and a map for non-locked state, as maps indicating correlations
between the operating point and the carrier frequency. The map for locked state may
be a map in which the carrier frequency in the lock region is set to the protection
frequency. The map for non-locked state may be a map in which the carrier frequency
is set to a frequency that is higher than the protection frequency, over an entire
range. The electronic control unit may be configured to select a reference map to
be referred to, from the map for locked state and the map for non-locked state, based
on the rotational speed of the motor and an acceleration of the motor, and determine
the carrier frequency based on the reference map.
[0012] With the above configuration, the two maps are selectively used according to the
motor rotational speed and acceleration. Thus, the process of determining the carrier
frequency can be simplified.
[0013] In the motor drive system, a hysteresis region in which a current frequency is used
as the carrier frequency may be set around the lock region, in the map for locked
state. The electronic control unit may be configured to determine that the motor is
in the accelerating or decelerating state, when an absolute value of the acceleration
of the motor is larger than a threshold value that is larger than zero.
[0014] With the above configuration, the threshold value used for determining the accelerating
or decelerating state is set to a value larger than zero, so that the possibility
of erroneously determining the locked state as the non-locked state can be reduced.
Also, when the threshold value is larger than zero, the operating point of the motor
moves little by little even when the motor is in the locked state. In this case, if
the hysteresis region is provided around the lock region in the map for locked state,
the frequency of change of the carrier frequency can be reduced.
[0015] A second aspect of the invention is concerned with a method of controlling a motor
drive system. The motor drive system includes a motor for driving a vehicle, an inverter,
and an electronic control unit. The inverter includes a plurality of switching devices,
and is configured to convert direct-current power into alternating-current power.
The method includes: generating, by the electronic control unit, a switching signal
of each of the switching devices, by performing, based on a carrier wave, pulse-width
modulation of a modulating wave indicating a command value for the motor; changing,
by the electronic control unit, a carrier frequency as a frequency of the carrier
wave according to operating conditions of the motor; setting, by the electronic control
unit, the carrier frequency to a protection frequency for protecting the switching
devices when the motor is in a first state in which an operating point determined
by a rotational speed of the motor and torque of the motor lies in a lock region that
is defined in advance, and the motor is not in an accelerating or decelerating state;
and setting, by the electronic control unit, the carrier frequency to a non-protection
frequency that is higher than the protection frequency when the motor is in a second
state in which the operating point lies in the lock region, and the motor is in the
accelerating or decelerating state.
[0016] With the above configuration, when the motor is in an accelerating or decelerating
state, the carrier frequency is set to the non-protection frequency even when the
motor operating point lies in the lock region. It is thus possible to prevent a noise
problem that would arise when the motor operating point temporarily enters the lock
region in the course of acceleration or deceleration, and the carrier frequency is
changed to the protection frequency. Also, with the above configuration, no temperature
sensor is needed, and the number of components can be prevented from being increased.
[0017] With the motor drive system described in this specification, even when the motor
operating point is in the lock region, the carrier frequency is set to the non-protection
frequency when the motor is in an accelerating or decelerating state. Thus, noise
is prevented from being temporarily generated in the course of acceleration or deceleration.
Also, the above configuration does not require a temperature sensor, and therefore,
the number of components can be prevented from being increased. As a result, it is
possible to achieve both prevention of overheating of the switching devices and prevention
of unnecessary noise, without requiring a temperature sensor to be added.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] Features, advantages, and technical and industrial significance of exemplary embodiments
of the invention will be described below with reference to the accompanying drawings,
in which like numerals denote like elements, and wherein:
FIG. 1 is a view showing the configuration of a motor drive system;
FIG. 2 is a functional block diagram of an electronic control unit;
FIG. 3 is a view showing one example of a map for non-locked state;
FIG. 4 is a view showing one example of a map for locked state;
FIG. 5 is a flowchart illustrating the flow of a map selection process; and
FIG. 6 is a view showing another example of a map for locked state.
DETAILED DESCRIPTION OF EMBODIMENTS
[0019] The configuration of a motor drive system 10 will be described with reference to
the drawings. FIG. 1 shows the configuration of the motor drive system 10. The motor
drive system 10 drives a motor 100 as one of power sources of an electrically powered
vehicle (such as a hybrid vehicle, or an electric vehicle), under pulse-width modulation
(PWM) control. The motor 100, which generates traveling power, is installed on the
vehicle. The motor 100 is a three-phase motor, and has three-phase coils. The motor
100 may also function as a generator that generates electric power by using excess
power of an engine (not shown) or braking force of the vehicle.
[0020] Current sensors 24 are mounted to coils of two phases (U phase and V phase in the
illustrated example), as a part of the three-phase coils, and serve to detect electric
current flowing through the coils. Current detection values iu, iv obtained by the
current sensors 24 are transmitted to an electronic control unit 14. The motor 100
is also provided with a position sensor (such as a resolver, not shown) that detects
the position of a rotor of the motor 100, and the position (rotational angle θ) detected
by the position sensor is transmitted to the electronic control unit 14.
[0021] An inverter 12 that converts direct-current (DC) power into alternating-current (AC)
power is connected to one end of each of the three-phase coils. Also, a smoothing
capacitor 18 and a power supply 16 are connected in parallel to the inverter 12. Here,
the power supply 16 may be a secondary battery capable of charge and discharge, or
may be a power storing means, such as a capacitor.
[0022] The inverter 12 consists of three (three-phase) arms 20 connected in parallel. Two
switching devices 22 are connected in series to each of the arms 20. Each of the switching
devices 22 has a transistor, such as an insulated gate bipolar transistor (IGBT),
and a flyback diode connected in parallel to the transistor. In operation, the upper
transistor is turned on, so that current flows into a corresponding one of the coils,
and the lower transistor is turned on, so that current flows out of the corresponding
coil.
[0023] The electronic control unit 14 controls driving of the inverter 12. The electronic
control unit 14 receives the current detection values iu, iv and the rotational angle
θ, as described above. The electronic control unit 14 also receives the amounts of
operation of an accelerator pedal and a brake pedal of the vehicle, vehicle acceleration,
and so forth, from a higher-level control unit. The vehicle acceleration is detected
by an acceleration sensor provided in the vehicle. The electronic control unit 14
produces a switching signal of the inverter 12, based on these items of information,
and switches the switching devices 22 between ON and OFF.
[0024] The electronic control unit 14, which is a microcomputer, for example, physically
has a central processing unit (CPU) that performs various computations, and a memory
that stores various kinds of information and programs. FIG. 2 is a functional block
diagram of the electronic control unit 14.
[0025] A torque command generating unit 30 calculates a torque command T*, namely, required
power (target output torque) of the motor 100, based on information, such as the operation
amounts of the accelerator pedal and brake pedal, received from a higher-level control
unit. The torque command T* thus calculated is supplied to a current command generating
unit 32 and a frequency determining unit 44. The current command generating unit 32
calculates a d-axis current command id* and a q-axis current command iq*, based on
the torque command T*. The d-axis current command id* and q-axis current command iq*
thus calculated are supplied to a PI controller 34.
[0026] In the meantime, the rotor rotational angle θ of the motor 100 and the current detection
values iu, iv currently obtained are supplied to a three-phase/two-phase converting
unit 36. The three-phase/two-phase converting unit 36 calculates a current detection
value iw of the W phase, from the current detection values iu, iv, and converts the
three-phase current detection values iu, iv, iw, into a d-axis current detection value
id and a q-axis current detection value iq. The d-axis current detection value id
and q-axis current detection value iq thus obtained are also supplied to the PI controller
34.
[0027] The PI controller 34 calculates a d-axis voltage command vd* and a q-axis voltage
command vq*, based on the d-axis and q-axis current commands id*, iq* and the d-axis
and q-axis current detection values id, iq. The PI controller 34 calculates the voltage
commands vd*, vq*, through feedback control, such as P (proportional) control, and
I (integral) control. It is, however, to be noted that this calculation method is
merely an example, and the d-axis and q-axis voltage commands vd*, vq* may be calculated
through other control, such as P control, or PID (proportional-integral-derivative)
control. Also, feedforward control, such as prediction control, may be combined with
the feedback control.
[0028] The d-axis and q-axis voltage commands vd*, vq* thus calculated are supplied to a
two-phase/three-phase converting unit 38. The two-phase/three-phase converting unit
38 converts the d-axis and q-axis voltage commands vd*, vq* into three-phase voltage
commands vu", vv", vw". The three-phase voltage commands vu*, vv*, vw* are supplied
to a PWM modulating unit 40.
[0029] The PWM modulating unit 40 generates switching signals Ss of the switching devices
22 in the inverter 12, by comparing modulating waves indicating the voltage commands
vu*, vv*, vw* with a carrier wave. The carrier wave is, for example, a triangular
wave, and is generated by a carrier wave generating unit 42. The inverter 12 is switched
based on the switching signals Ss, so that desired current flows into the motor 100.
[0030] The frequency of the carrier wave (which will be called "carrier frequency fc") is
determined by the frequency determining unit 44. Also, two types of maps, namely,
a map 50 for non-locked state and a map 52 for locked state are stored in a map storage
unit 46. The frequency determining unit 44 determines the carrier frequency fc, referring
to these maps 50, 52.
[0031] The manner of determining the carrier frequency fc will be described. FIG. 3 shows
one example of the map 50 for non-locked state, and FIG. 4 shows one example of the
map 52 for locked state. In FIG. 3 and FIG. 4, the horizontal axis indicates the rotational
speed Nm of the motor 100, and the vertical axis indicates the torque T of the motor
100.
[0032] Both the map 52 for locked state and the map 50 for non-locked state show correlations
between operating points defined by the rotational speed Nm of the motor and the torque
T, and the carrier frequency fc. As is apparent from FIG. 3 and FIG. 4, in this example,
there are three different frequencies F1, F2, F3 (F1>F2>F3) as candidates of the carrier
frequency fc. The frequency F3 is a frequency determined in view of prevention of
overheating of the switching devices 22, and is significantly lower than the two frequencies
F1, F2. In the following description, the frequency F3 will be called "protection
frequency F3". The protection frequency F3 is, for example, 1.5 kHz or lower. The
frequencies F1, F2 are higher than the protection frequency F3, and are determined
in view of noise prevention. In the following description, each of the frequencies
F1, F2 will be simply called "non-protection frequency" when they are not distinguished
from each other. The non-protection frequency is, for example, 2 kHz or higher.
[0033] In the map 50 for non-locked state, the carrier frequency fc is set to a non-protection
frequency (F1 or F2) over the entire range. In the map 50 for non-locked state, the
carrier frequency fc is set to be lower as the motor torque T is larger. More specifically,
in the example of FIG. 3, a region in which the motor torque T is equal to or smaller
than a specified value Tc is a high-frequency region, irrespective of the motor speed
Nm. When the operating point of the motor lies in this high-frequency region, the
carrier frequency fc is set to F1 as a relatively high frequency. A region in which
the motor torque Tm is equal to or larger than a specified value Td (Td>Tc) is a low-frequency
region, irrespective of the motor speed Nm. When the operating point of the motor
lies in the low-frequency region, the carrier frequency fc is set to F2 as a frequency
lower than F1.
[0034] A region in which the motor torque T is larger than the specified value Tc and is
smaller than the specified value Td is a hysteresis region. When the operating point
of the motor lies in the hysteresis region, the carrier frequency fc is kept at the
current carrier frequency fc. For example, in FIG. 3, when the operating point of
the motor 100 moves from point P1 in the low-frequency region to point P2 in the hysteresis
region, the carrier frequency fc remains to be the frequency F2. Also, when the operating
point of the motor moves from point P3 in the high-frequency region to point P2 in
the hysteresis region, the carrier frequency fc remains to be the frequency F1.
[0035] The map 52 for locked state is a map that is referred to when the motor 100 is highly
likely to be in a locked state in which rotation of the motor 100 is disturbed or
hampered by external force. In the map 52 for locked state, the carrier frequency
fc in a lock region is set to the protection frequency F3. More specifically, in the
example of FIG. 4, a region in which the motor speed Nm is equal to or lower than
a specified value Nb, and the motor torque T is equal to or larger than Tb provides
the lock region. When the motor operating point lies in the lock region, the carrier
frequency fc is set to the sufficiently low protection frequency F3.
[0036] A hysteresis region is set around the lock region. More specifically, the hysteresis
region is a part of a region in which the motor torque T is equal to or larger than
Ta, and the motor speed Nm is equal to or lower than Na, and excludes the lock region.
When the operating point of the motor 100 is in the hysteresis region, the carrier
frequency fc is kept at the current frequency fc.
[0037] Here, the reason why the lock region is provided will be described. The motor 100
is in the locked state, when rotation of the motor 100 is disturbed or hampered by
external force, and the motor 100 stops rotating, or is rotating at an extremely low
speed. When the motor 100 is placed in the locked state, electric current concentrates
in only one-phase winding, out of the windings provided in the motor 100. In this
case, the switching devices 22 corresponding to the one phase, among the switching
devices 22 provided in the inverter 12, rapidly generate heat, and may be damaged
or deteriorated in some cases.
[0038] In order to prevent overheating of the switching devices 22, it has been proposed
to set the carrier frequency fc to a significantly low protection frequency F3 when
the operating point of the motor 100 is in the lock region. In this manner, the switching
frequency is reduced, and a loss of the switching devices 22 is reduced. As a result,
heat generated by the switching devices 22 is reduced. In this example, however, even
when the motor 100 is locked, and stops rotating or rotates at a low speed (Nm<Nb),
the carrier frequency fc is set to the relatively high frequency F1 when the torque
T is smaller than Tb. This is because, even when the motor 100 is locked, the amount
of current passing through the motor 100, or the amount of heat generated, is small,
and the possibility of overheating is small, when the motor torque T is small.
[0039] The frequency determining unit 44 selects one of the map 52 for locked state and
the map 50 for non-locked state, based on the current operating conditions of the
motor 100, and determines the carrier frequency fc, by checking the current operating
point of the motor 100 against the selected map. The motor speed Nm may be calculated
from the rotor rotational angle θ, or may be calculated from the vehicle speed. More
specifically, the motor angular velocity may be calculated by differentiating the
rotor rotational angle θ, and the motor angular velocity may be converted into the
rotational speed Nm. Alternatively, the motor speed Nm may be calculated from the
vehicle speed, since the motor speed and the vehicle speed are in a proportional relationship
with each other. Also, in this example, the torque command value T* generated by the
torque command generating unit 30 is regarded as the motor torque T. However, the
motor torque may be calculated from the current detection values, in place of the
torque command value T*, or the motor 100 may be provided with a torque sensor.
[0040] In the related art, the carrier frequency fc is set, referring only to the map 52
for locked state, without switching between the map 50 for non-locked state and the
map 52 for locked state. Thus, when the motor operating point is located in the lock
region, the carrier frequency fc is always set to the protection frequency F3. Accordingly,
when the motor operating point passes the lock region only temporarily, in the course
of acceleration or deceleration of the motor 100, the carrier frequency fc is also
switched to the protection frequency F3 only temporarily.
[0041] However, in this case, there is a problem that unnecessary noise is generated. Namely,
the non-protection frequencies F1, F2 established when the motor 100 is not locked
are normally set to high frequencies (e.g., equal to or higher than 2 kHz) at which
electromagnetic resonance of the motor 100 does not fall within an audible area. On
the other hand, the protection frequency F3 is set to a sufficiently low value (e.g.,
1.5 kHz or lower), with more emphasis placed on reduction of heat generated by the
switching devices 22, rather than reduction of noise, and the electromagnetic resonance
of the motor 100 may fall within the audible area at the protection frequency F3.
[0042] Therefore, if the carrier frequency fc is switched to the protection frequency F3
only temporarily, during acceleration or deceleration of the motor 100, as described
above, noise caused by the electromagnetic resonance of the motor 100, etc., is increased
temporarily, and an occupant of the vehicle may feel strange or uncomfortable, even
though there is no particular problem in the motor 100.
[0043] Thus, it has been proposed, as a part of the related art, to measure the temperature
(device temperature) of each switching device 22 with a temperature sensor, and determine
whether the carrier frequency fc is to be switched to the protection frequency F3,
in view of the device temperature. According to this technology, when the operating
point of the motor 100 passes the lock region only temporarily, the carrier frequency
fc is not switched to the protection frequency F3. As a result, unnecessary noise
is prevented from being generated. However, this technology makes it necessary to
provide the temperature sensor for detecting the temperature of each switching device
22, resulting in increase of the number of components. The increase of the number
of components incurs increase of the component cost, and increase of the number of
process steps for maintenance.
[0044] Thus, in this embodiment, when the motor is in an accelerating or decelerating state,
it is determined that the motor is not locked even when the operating point of the
motor 100 lies in the lock region, and the carrier frequency fc is set to the frequency
F1 or F2 that is higher than the protection frequency F3. More specifically, in this
embodiment, the map 52 for locked state, in which the lock region is provided, and
the map 50 for non-locked state, in which the lock region is not provided, are prepared,
and the map to be referred to is selected according to the rotational speed Nm and
acceleration Am of the motor. Here, the motor speed Nm and the acceleration Am may
be obtained by differentiating the rotor rotational angle θ or differentiating it
twice. The vehicle is normally provided with a vehicle speed sensor that detects the
vehicle speed, and an acceleration sensor that detects the acceleration of the vehicle.
Accordingly, the motor speed Nm and acceleration Am may be calculated from detection
values of the vehicle speed sensor and acceleration sensor.
[0045] FIG. 5 is a flowchart illustrating the flow of a process of selecting a map by the
frequency determining unit 44. As shown in FIG. 5, the frequency determining unit
44 initially determines whether the motor rotational speed Nm is equal to or lower
than a specified threshold value Ndef (S10). The threshold value Ndef is not particularly
limited provided that it is equal to or higher than the maximum rotational speed Na
of the hysteresis region set around the lock region; however, the threshold value
Ndef is desirably set to Na, for simplicity of the process.
[0046] When the motor speed Nm is higher than the threshold value Ndef, there is no possibility
that the motor 100 is in the locked state; therefore, the frequency determining unit
44 determines the carrier frequency fc, referring to the map 50 for non-locked state
(S16). On the other hand, when the motor speed Nm is equal to or lower than the threshold
value Ndef, the frequency determining unit 44 subsequently determines whether the
motor is in an accelerating or decelerating state (S12). More specifically, the frequency
determining unit 44 determines whether the absolute value of the motor acceleration
Am is larger than a specified threshold value Adef. The threshold value Adef is not
particularly limited provided that it is equal to or larger than zero; however, it
is desirable to set the threshold value Adef to a value of a certain magnitude, which
is larger than zero, so as to prevent the locked state from being erroneously determined
as the non-locked state.
[0047] When the motor acceleration Am is larger than the threshold value Adef, the frequency
determining unit 44 can determine that the motor 100 is not in the locked state, and
thus determines the carrier frequency fc, referring to the map 50 for non-locked state
(S16). Accordingly, in this case, even if the motor operating point is located in
the lock region, the carrier frequency fc is set to the frequency F1, F2 other than
the protection frequency.
[0048] When the motor acceleration Am is equal to or smaller than the threshold value Adef,
the motor 100 may be in the locked state; therefore, the frequency determining unit
44 sets the carrier frequency fc, referring to the map 52 for locked state (S14).
Accordingly, in this case, if the motor operating point is located in the lock region,
the protection frequency F3 is set as the carrier frequency fc.
[0049] Here, some case examples will be studied. First, the case where the operating point
of the motor 100 moves from point P6 to points P5, P4, P3, at an acceleration equal
to or larger than the threshold value Adef, will be considered. In this case, since
the motor acceleration Am exceeds the threshold value Adef, the frequency determining
unit 44 determines that the carrier frequency fc is equal to F1, referring to the
map 50 for non-locked state.
[0050] Also, suppose the operating point of the motor 100 moves from point P5 to point P4,
at an acceleration equal to or smaller than the threshold value Adef, after moving
from point P6 to point P5 at an acceleration exceeding the threshold value Adef. In
this case, during a period in which the operating point of the motor 100 moves from
point P6 to P5, the frequency determining unit 44 determines that the carrier frequency
fc is equal to F1, referring to the map 50 for non-locked state. On the other hand,
during a period in which the operating point of the motor 100 moves from point P5
to point P4, the frequency determining unit 44 determines that the carrier frequency
fc is equal to F3, referring to the map 52 for locked state.
[0051] Next, the case where the operating point of the motor 100 moves from point P3 to
point P4, at an acceleration of which the absolute value |Am| is larger than the threshold
value Adef, and then moves from point P4 to point P5, at an acceleration of which
the absolute value |Am| is equal to or smaller than the threshold value Adef. In this
case, during a period of movement from point P3 to point P4, the frequency determining
unit 44 determines that the carrier frequency fc is equal to F1, referring to the
map 50 for non-locked state. Also, during a period of movement from point P4 to point
P5, the frequency determining unit 44 determines the carrier frequency fc, referring
to the map 52 for locked state. In this case, the carrier frequency fc is equal to
F1, since the current frequency is maintained, until the operating point moves from
point P4 and comes out of the hysteresis region. On the other hand, the carrier frequency
fc is equal to F3, during a period in which the operating point comes out of the hysteresis
region and moves to point P5.
[0052] As is apparent from the above description, in this embodiment, when the motor 100
is in an accelerating or decelerating state, the non-protection frequency F1 or F2
is set as the carrier frequency fc, even if the motor operating point lies in the
lock region. As a result, unnecessary noise can be prevented from being generated.
Also, in this embodiment, whether the protecting frequency F3 needs to be set is determined,
based on the motor acceleration Am (or the vehicle acceleration). Therefore, there
is no need to add a new component, such as a temperature sensor, and the number of
components can be prevented from being increased.
[0053] The configuration as described above is merely an example. Provided that the carrier
frequency fc is set to a higher frequency in the case where the motor 100 is in an
accelerating or decelerating state, than that in the case where the motor 100 is not
in an accelerating or decelerating state, even when the operating point is in the
lock region, the other configuration may be changed as appropriate. For example, while
a single threshold value Adef is used when determining whether the motor 100 is in
an accelerating or decelerating state, the threshold value may be given certain hysteresis.
More specifically, two threshold values Adefl, Adef2 (Adef2>Adefl) may be provided
for determination of the accelerating or decelerating state, and the map 52 for locked
state may be referred to when the motor acceleration Am is equal to or smaller than
Adefl, while the map 50 for non-locked state may be referred to when the motor acceleration
Am exceeds Adef2. Also, the map that is currently referred to may continue to be referred
to, when the motor acceleration Am is larger than Adefl, and is equal to or smaller
than Adef2. With this arrangement, the frequency of switching of the reference maps
can be reduced, and the carrier frequency fc is less likely to be changed.
[0054] In the example of FIG. 4, the hysteresis region is provided around the lock region,
in the map 52 for locked state. However, when the threshold value Adef as a criterion
for determination of the accelerating or decelerating state is set to a sufficiently
small value, the hysteresis region may be eliminated in the map 52 for locked state,
as shown in FIG. 6. Namely, when the threshold value Adef is set to a sufficiently
small value, the motor 100 is determined as being in a non-locked state if the rotational
speed changes just a little, and the map 50 for non-locked state is referred to. In
this case, there is no need to provide a hysteresis region around the lock region,
and the hysteresis region may be eliminated. Also, in this embodiment, the operating
range of the motor 100 is divided into two regions in the map for non-locked state,
and two non-protection frequencies F1, F2 are set for the two regions. However, the
operating range of the motor 100 may be divided into a larger number of regions, or
may be only a single region, in the map for non-locked state.
[0055] While two kinds of maps 50, 52 are selectively used in this embodiment, maps may
not be used, provided that a higher carrier frequency fc is selected in the case where
the motor 100 is in an accelerating or decelerating state, than that in the case where
the motor 100 is not in an accelerating or decelerating state, even when the motor
operating point is in the lock region.
1. Motorantriebssystem (10), umfassend:
einen Motor (100) zum Antreiben eines Fahrzeugs,
einen Wechselrichter (12), der mehrere Schaltvorrichtungen (22) beinhaltet und dazu
ausgestaltet ist, Gleichstromenergie in Wechselstromenergie umzuwandeln, und
eine elektronische Steuereinheit (14), die dazu ausgestaltet ist, ein Schaltsignal
jeder der Schaltvorrichtungen (22) zu erzeugen, indem basierend auf einer Trägerwelle
eine Pulsweitenmodulation einer Modulationswelle ausgeführt wird, die einen Befehlswert
für den Motor (100) anzeigt,
wobei die elektronische Steuereinheit (14) dazu ausgestaltet ist, eine Trägerfrequenz
als eine Frequenz der Trägerwelle gemäß den Betriebsbedingungen des Motors (100) zu
ändern,
die elektronische Steuereinheit (14) dazu ausgestaltet ist, die Trägerfrequenz auf
eine Schutzfrequenz (F3) zum Schutz der Schaltvorrichtungen (22) einzustellen, wenn
sich der Motor (100) in einem ersten Zustand befindet, in dem ein Betriebspunkt, der
durch eine Drehzahl des Motors (100) und ein Drehmoment des Motors (100) bestimmt
wird, in einem Sperrbereich liegt, der im Voraus definiert wird,
dadurch gekennzeichnet, dass:
der Motor (100) sich in dem ersten Zustand nicht in einem Beschleunigungs- oder Verlangsamungszustand
befindet, und
die elektronische Steuereinheit (14) dazu ausgestaltet ist, die Trägerfrequenz auf
eine Nichtschutzfrequenz (F1; F2) einzustellen, die höher als die Schutzfrequenz (F3)
ist, wenn sich der Motor (100) in einem zweiten Zustand befindet, in dem der Betriebspunkt
in dem Sperrbereich liegt, und der Motor (100) sich in dem Beschleunigungs- oder Verlangsamungszustand
befindet.
2. Motorantriebssystem (10) nach Anspruch 1, wobei:
die elektronische Steuereinheit (14) dazu ausgestaltet ist, eine Karte für den gesperrten
Zustand und eine Karte für den nicht gesperrten Zustand als Karten zu speichern, die
Korrelationen zwischen dem Betriebspunkt und der Trägerfrequenz anzeigen, wobei die
Karte für den gesperrten Zustand eine Karte ist, bei der die Trägerfrequenz in dem
Sperrbereich auf die Schutzfrequenz eingestellt wird, wobei die Karte für den nicht
gesperrten Zustand eine Karte ist, bei der die Trägerfrequenz auf eine Frequenz eingestellt
wird, die höher als die Schutzfrequenz über einen gesamten Bereich ist, und
die elektronische Steuereinheit (14) dazu ausgestaltet ist, eine Referenzkarte, auf
die Bezug genommen werden soll, aus der Karte für den gesperrten Zustand und der Karte
für den nicht gesperrten Zustand basierend auf der Drehzahl des Motors (100) und einer
Beschleunigung des Motors (100) auszuwählen und die Trägerfrequenz basierend auf der
Referenzkarte zu bestimmen.
3. Motorantriebssystem (10) nach Anspruch 2, wobei:
ein Hysteresebereich, in dem eine aktuelle Frequenz als die Trägerfrequenz verwendet
wird, um den Sperrbereich in der Karte für den gesperrten Zustand eingestellt wird,
und
die elektronische Steuereinheit (14) dazu ausgestaltet ist, zu bestimmen, dass sich
der Motor (100) in dem Beschleunigungs- oder Verlangsamungszustand befindet, wenn
ein Absolutwert der Beschleunigung des Motors (100) größer als ein Schwellenwert ist,
der größer als null ist.
4. Verfahren zum Steuern eines Motorantriebssystems (10), wobei das Motorantriebssystem
(10) einen Motor (100) zum Antreiben eines Fahrzeugs, einen Wechselrichter (12) und
eine elektronische Steuereinheit (14) beinhaltet, wobei der Wechselrichter (12) mehrere
Schaltvorrichtungen (22) beinhaltet und dazu ausgestaltet ist, Gleichstromenergie
in Wechselstromenergie umzuwandeln,
wobei das Verfahren umfasst:
Erzeugen eines Schaltsignals jeder der Schaltvorrichtungen (22) durch die elektronische
Steuereinheit (14) durch Ausführen einer Pulsweitenmodulation einer Modulationswelle
basierend auf einer Trägerwelle, die einen Befehlswert für den Motor (100) anzeigt,
Ändern einer Trägerfrequenz als eine Frequenz der Trägerwelle gemäß den Betriebsbedingungen
des Motors (100) durch die elektronische Steuereinheit (14),
Einstellen der Trägerfrequenz auf eine Schutzfrequenz (F3) durch die elektronische
Steuereinheit (14) zum Schutz der Schaltvorrichtungen (22), wenn sich der Motor (100)
in einem ersten Zustand befindet, in dem ein durch eine Drehzahl des Motors (100)
und ein Drehmoment des Motors (100) bestimmter Betriebspunkt in einem Sperrbereich
liegt, der im Voraus definiert wird,
dadurch gekennzeichnet, dass: sich der Motor (100) in dem ersten Zustand nicht in einem Beschleunigungs- oder
Verlangsamungszustand befindet, und dass das Verfahren umfasst:
Einstellen der Trägerfrequenz durch die elektronische Steuereinheit (14) auf eine
Nichtschutzfrequenz (F1; F2), die höher als die Schutzfrequenz (F3) ist, wenn sich
der Motor (100) in einem zweiten Zustand befindet, in dem der Betriebspunkt in dem
Sperrbereich liegt, und sich der Motor (100) in dem Beschleunigungs- oder Verlangsamungszustand
befindet.